feat(fe+be): 身份卡头像不再压扁 + 内容丰富

- 头像用九参数 drawImage 居中裁剪（cover），竖图/横图都不变形，加白边圈
- 后端 IDCard 增 zodiac(按生日算星座) + weight，卡面加「星座/体重」行
- 加淡淡的肉垫水印 + 旋转的「肉垫计划·官方认证」印章
- 画布加高容纳新增内容

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

pets-be/internal/service/idcard.go

@@ -14,6 +14,8 @@ type IDCard struct {
 	Gender    string `json:"gender"`
 	Breed     string `json:"breed"`
 	Birthday  string `json:"birthday"` // "2023 年 12 月 15 日"
+	Zodiac    string `json:"zodiac"`   // 星座，按生日算
+	Weight    string `json:"weight"`   // 体重，如 "13.5kg"
 	Intro     string `json:"intro"`
 	AvatarURL string `json:"avatar_url"`
 	IDNo      string `json:"id_no"`    // 玩具身份号，不入库
@@ -51,6 +53,26 @@ func petIDNo(pet *model.Pet) string {
 	return b.String()
 }
 
+// zodiacOf 按月日算西方星座。按各星座起始日（含）顺序判定，
+// 落在 12/22–1/19 的默认摩羯座
+func zodiacOf(month, day int) string {
+	starts := []struct {
+		m, d int
+		name string
+	}{
+		{1, 20, "水瓶座"}, {2, 19, "双鱼座"}, {3, 21, "白羊座"}, {4, 20, "金牛座"},
+		{5, 21, "双子座"}, {6, 22, "巨蟹座"}, {7, 23, "狮子座"}, {8, 23, "处女座"},
+		{9, 23, "天秤座"}, {10, 24, "天蝎座"}, {11, 22, "射手座"}, {12, 22, "摩羯座"},
+	}
+	name := "摩羯座"
+	for _, s := range starts {
+		if month > s.m || (month == s.m && day >= s.d) {
+			name = s.name
+		}
+	}
+	return name
+}
+
 // GetIDCard 组装身份卡。小程序码是 best-effort：拿不到（未发布/配额）也照出卡
 func (s *Service) GetIDCard(userID, petID string) (*IDCard, error) {
 	pet, err := s.GetPet(userID, petID)
@@ -72,10 +94,15 @@ func (s *Service) GetIDCard(userID, petID string) (*IDCard, error) {
 		validity = pet.Birthday.Format("2006.01.02") + " - 永远"
 	}
 
+	zodiac := ""
+	if pet.Birthday != nil && !pet.Birthday.IsZero() {
+		zodiac = zodiacOf(int(pet.Birthday.Month()), pet.Birthday.Day())
+	}
+
 	card := &IDCard{
 		Name: pet.Name, Species: pet.Type, Gender: pet.Gender, Breed: pet.Breed,
-		Birthday: bd, Intro: intro, AvatarURL: pet.AvatarURL,
-		IDNo: petIDNo(pet), Validity: validity,
+		Birthday: bd, Zodiac: zodiac, Weight: pet.Weight, Intro: intro,
+		AvatarURL: pet.AvatarURL, IDNo: petIDNo(pet), Validity: validity,
 	}
 
 	// 小程序码取不到不算错——未发布/配额用尽时卡照样出，只是没码